Even with the argument that we absolutely and desperately need more tanks to make queues easier for DPS and assuming that it is an absolute necessity to do this,
I still think that Samurai as tank is a bad choice, even if it's popular. As i said, i don't doubt that some people will switch to tank full time on the long run, I don't think it will be a significant amount.

Rather than that, I still think the idea i mentioned of a Runefencer / Red Mage type of tank to be way more efficient for this purpose. I know it might sound weird when i bring up Red Mage for this,
but at least in my opinion the concept of a magical tank that works with putting up barriers to mitigate damage, in a similar fashion as to the Scholar's Adloquium shields sounds really interesting.
These wouldn't necessarily be cooldowns, but abilities that can be triggered upon weaponskill execution, since they are jack of all trades, after all. Offensive abilities could also be an alternative instead of defensive shields.

The reason i think this path to be way more efficient is because it would bring something entirely new to the tanking lineup, something that would also be interesting for people interested in caster-type gameplay.
We already have 3 melee tanks that are only capable of attacking with physical attacks.
All pretty much all of them rely on block / parry procs besides defensive cooldowns, War is most interesting even in my opinion with Inner Beast being a form of mitigation that doesn't rely on a cooldown really.

Adding such a tank that relies on magic for defense and offense would contribute more to adding more career tanks in the long run in my opinion.